1. Field of the Invention
The invention relates to an electromagnetic induction coil unit for use in a heating apparatus of the electromagnetic induction heating type for heating a material to be heated by the heat generation of an electromagnetic induction heat generative member, and a method of manufacturing the same.
Here, the heating apparatus using the electromagnetic induction coil unit of the present invention can be widely utilized not only as an image heating and fixing apparatus like an embodiment as will be described later, but also as a heating apparatus for a material to be heated, such as an image heating apparatus for heating a recording material bearing an image thereon to thereby improve the surface property (such as glossing), an image heating apparatus for provisionally heating an image, or a heating apparatus for executing heat press, drying process, laminating process, etc. while conveying a sheet-like material.
2. Description of Related Art
For example, an image forming apparatus using the electrophotographic process is usually provided with a fixing device as an image heating apparatus for fusion-bonding a toner image on a recording material such as transfer paper. A conventional fixing device is comprised of heating means for heating and fusion-bonding a toner image, and pressurizing means for nipping and conveying the recording material while pressing it.
Also, the heating means has generally been provided with a halogen lamp as a heater in a heating roller, and has heated the heating roller by the lamp and has raised the temperature thereof to a temperature necessary for fixing.
In such a fixing device, a method of generating an eddy current in an electrically conducting layer provided on the surface of a fixing roller by a magnetic flux by an electromagnetic induction coil, and causing the fixing roller to generate heat by Joule heat has been proposed as means for heating (Japanese Patent Application Laid-Open No. 2000-081806). This method enables a heat generating source to be placed very close to a toner image and therefore, as compared with the conventional heat roller type using the halogen lamp, it has the feature that the time required until at the starting of the fixing device, the temperature of the surface of the fixing roller reaches a temperature suitable for fixing can be shortened.
As the general construction of the heat roller in the fixing device of the electromagnetic induction heating type, there is known one provided with a bobbin having an electromagnetic induction coil spirally wound in a heat roller comprising a metal conductor (Japanese Patent Application Laid-Open No. 2000-173759).
While a material excellent in electrical conductivity is used as the material of the electromagnetic induction coil, heat generation may sometimes become great even in a highly electrically conductive material by a heavy current of a high frequency.
Further, the heating efficiency of the fixing roller has sometimes become bad when the electromagnetic induction coil is overheated. Therefore, it is necessary to efficiently discharge the overheat of the induction coil to the outside, but there has been the problem that the bobbin on which the electromagnetic induction coil is wound is liable to be fitted with heat.
Accordingly, a construction in which the bobbin on which the coil is wound is eliminated so that the cooling effect for the electromagnetic induction coil may become high, and the overheat of the electromagnetic induction coil is efficiently discharged to the outside. As a bobbinless coil, there is known a molded coil resin-enveloped by molding (Japanese Patent Application Laid-Open No. 05-049201), and the entire electromagnetic induction coil is covered with resin of good heat conductivity to thereby enhance the radiating property of the coil.
In a manufacturing method therefore, however, there is the problem that during formation, the coil is deformed or moved by the injection pressure and flowing of the molded resin.
Heretofore, a method of manufacturing an insert article such as a molded coil has been carried out by the use of a metal mold having a pin for holding the insert article, as shown in FIG. 19 of the accompanying drawings (Japanese Patent Application Laid-Open No. 08-072099).
Describing the specification of this metal mold, a metal mold space (cavity) 24 is formed between a closed fixed side metal mold 15 and a movable side metal mold 16, and a holding pin 26 for holding an insert part 21 at a predetermined location in the metal mold space 24 has one end thereof fixed to a plate 25 and the other end thereof inserted for forward and backward movement in a through-hole formed in the metal mold. A rod 22 and an actuator 23 are installed to effect the control of the forward and backward movement of this holding pin 26.
Describing a manufacturing method in this case, the following procedures are repeated.
1. The metal molds 15 and 16 are placed in their opened state and the holding pin 26 is moved forward to a predetermined position.
2. The insert part 21 is held by the holding pin 26 stopped at the predetermined position.
3. The metal molds 15 and 16 are closed.
4. Molten resin is poured into the metal mold space 24 through a runner and a gate.
5. The holding pin 26 is moved backward to a predetermined position.
6. Molten resin is further poured, and molten resin is also poured into a clearance portion formed by the backward movement of the holding pin 26.
7. The molten resin poured into the metal mold space 24 is cooled and solidified.
8. The metal molds 15 and 16 are opened.
9. The molded article of the insert part 21 is taken out of the metal mold.
However, in the case of an insert part of large dimension (an elliptical coil greatly differing in the aspect ratio) like an electromagnetic induction coil which is the basic construction of an electromagnetic induction coil unit to which the present invention is directed, to completely fix it in the metal mold space 24, it is necessary to use considerably many holding pins 26, and the structure of the metal mold becomes complicated.
Also, one of the purposes of resin-enveloping the electromagnetic induction coil is to secure the thickness of the resin molded portion equal to or greater than a required value (determined by the electrical safety standard) in order to ensure electrical safety (electrical insulation).
However, when the holding by the holding pin 26 of the electromagnetic induction coil which is an insert part is insufficient, the thickness of the formed resin molded portion becomes non-uniform due to the deformation and movement of the electromagnetic induction coil, and this also leads to the problem that the thickness cannot be ensured.
Further, for the purpose of improving electrical safety, it is required that the electromagnetic induction coil be hermetically sealed by resin.
However, if the timing for backwardly moving the holding pin 26 from the metal mold space 24 is bad, a cooled and solidified layer will be formed on the resin around the holding pin, and this leads to the problem that the resin having flowed from around the holding pin into a pin hole is not completely fused but the hole remains and a resin molded portion which has completely enveloped the coil cannot be formed.
On the other hand, in a method of manufacturing an electromagnetic induction coil unit of the resin-enveloped type, in order to lead the lead wire of the electromagnetic induction coil out of an enveloping molded portion, provision is made of such a mechanism as will cause the lead wire to be held by a metal mold, and the covering material of the lead wire is compressed and held during the mold fastening of the metal mold to thereby prevent the leakage of resin from the lead wire portion (Japanese Patent Application Laid-Open No. 07-142278).
However, when a coil holder, an electromagnetic induction coil and a coil holding-down member are used as basic constituents and the electromagnetic induction coil is enveloped by insulating resin, it has been difficult to obtain a good bonded state in the joint surface between the coil holder and a shape formed by envelope molding (hereinafter referred to as the envelope-molded member) and the joint surface between the coil holding-down member and the envelope-molded member.
Also, when an article low in rigidity like the electromagnetic induction coil is envelope-molded, the coil is compressed by the pressure of enveloping resin, but exfoliation from the joint surface occurs due to the reaction force (spring-back) thereof or exfoliation occurs on the joint surface due to the thermal impact by the temperature rise during use, and this leads to the problem that insulativeness is spoiled when the coil is used for a long time under a high-temperature and high-humidity environment.
In the manufacturing method for the electromagnetic induction coil unit, the metal mold is provided with such a mechanism as will compress and hold the lead wire of the electromagnetic induction coil to lead the lead wire out of the envelope-molded portion to thereby prevent the leakage of resin from the lead wire portion, but there is the problem that if the adjustment of the amount of compression of the covering material thereof and the accuracy of the metal mold are bad, the covering material of the lead wire will be greatly spoiled and the breaking of the lead wire or the leakage of resin will occur.